Soil has been used for construction for many hundreds of years. For instance, walls made of rammed earth and mud at Jiayuguan, China are said to have been built during the Ming Dynasty. Modern rammed earth walls are typically formed by first creating forms outlining the desired shape of a section of the wall. Damp soil that may be mixed with cement or other materials is then poured in to a depth of between 10 cm and 25 cm (4 to 10 inches). A pneumatically powered backfill tamper is then used to compact the soil to about one-half its original height. Further layers of soil are added and the process is repeated until the wall has reached the desired height.
Retaining walls for slopes are typically made of masonry, stone, brick, concrete, vinyl, steel or timber. A retaining wall can be made, for example, by pouring concrete into form boards that outline the wall. Also known is to make retaining walls with wide concrete slabs that are stacked on each other to form the wall. Geogrid reinforcement, a metal or plastic mesh that holds rocks or soil in place, can also be used to help secure a slope.